Antifoam compositions containing linear diorganopolysiloxanes such as dimethylpolysiloxanes have been widely used as defoamers in, for example, jet dyeing of textile materials.
Aqueous silicone emulsions containing dimethyl silicone fluids have been described, for example, in U.S. Pat. No. 4,194,988 to Schneider et al for defrothing purposes in which the dimethylpolysiloxanes are mixed with an emulsifier containing mono- or diesters of orthophosphoric acid until a clear solution is obtained and then an organic base or alkali is added to neutralize the clear solution.
Antifoam compositions for aqueous systems have been described in U.S. Pat. No. 3,666,681 to Keil, which contain (A) a water insoluble organic liquid such as a mineral oil, esters of carboxylic acids, monohydric alcohols, vegetable oils, polyoxypropylene and polyoxybutylene glycols; (B) an organopolysiloxane compound selected from a hydroxyl endblocked dimethylpolysiloxane fluid or a benzene soluble organopolysiloxane resin; (C) a silica filler; and (D) a compound selected from a hydrocarbon amine, ammonia or a disilazane.
An emulsion defoamer composition is also described in U.S. Pat. No. 4,225,456 to Schmidt et al which contains (A) hydrophobic silica; (B) an amide; (C) an organic polymer; (D) an emulsifier; (E) an oil, such as a mineral oil; (F) a silicone oil; and (G) water.
In contrast to the antifoam compositions described heretofore, the antifoam compositions of this invention have certain advantages. For example, emulsions of these antifoam compositions are more effective in an alkali medium and their effectiveness lasts for a longer period of time. Also, emulsions of this invention have a longer shelf-life, have better thermal stability and are more stable to mechanical stresses such as shear stresses. Moreover, the antifoam compositions of this invention are more effective in controlling foam formation in, for example, the evaporation of alkaline black liquor in the paper industry, textile dyeing, sewage disposal and in the concentration of synthetic rubber latices.
Therefore, it is an object of the present invention to provide a novel antifoaming composition which prevents or abates undesirable foaming in aqueous and nonaqueous systems. Another object of the present invention is to provide an antifoam composition having a longer shelf-life and better thermal stability. Still another object of the present invention is to provide an antifoam composition which is easily emulsified to form an aqueous or nonaqueous emulsion. A further object of the present invention is to provide an antifoam composition which is more effective in controlling foam formation.